There is no consensus on standard of care for treatment of subjects who have failed therapy with a protease inhibitor/dual NRTI regimen. New regimens may include drugs from entirely new classes of antiretroviral agents, or different drugs from within the same classes. The treatment regimens in this study were designed to incorporate a new class of drug, NNRTI (nevirapine) and new drugs from the previously employed classes, protease inhibitors and at least one new NRTI. This study will compare ABT378/Ritonavir vs. one or two different protease inhibitors, plus nevaripine and 2 NRTIs ( including at least one new NRTI). Subjects who have HIV RNA level of at least 1,000 copies/ml and at most 100,000 copies/ml while treated with a regimen consisting of a single protease inhibitor and two NRTIs that has not changed for at least twelve weeks will be randomized into this study.